Converting a long focus doublet for AP with a DSLR

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Kanadalainen
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Converting a long focus doublet for AP with a DSLR

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Post by Kanadalainen »


Impossible you say?

Impractical, perhaps?

Well you may have a point, but I have an old Celestron f6.3 FRFF in my sock drawer and wanted to see how it might be done.
I also have a C80, circa. mid-1990's, which is a very nice doublet. f11.3 and has a 910mm focal length - a beautiful scope for visual work on planets, DSOs and the moon. It has a newer 2" Crayford Focuser.

Wouldn't it be great to use this scope on an appropriate mount for some astro work? :)

The goal is to try to create an optical path that could be used for AP.

Problem 1. The Celestron f6.3 is made for SCT usage. Can it be adapted for a Crayford Focuser?
Problem 2. What is the sweet spot for the working length of this focal reducer? Can it be reached?

A1 - I think so, with the right adaptors. I looked to Scopestuff for this.
A2 - The working length may be around 106 mm (total from glass to sensor), but the beauty of the design of this FRFF is that you have some room to play. ~ 36mm of this is taken up within the body of the camera itself. Knowing this and having a few adaptors in hand, empircal testing is possible.

Here is the beginning of what I have put together. This image shows my D90 Nikon, but any DSLR could be used here, with the right T-fitting.

Camera - t-mount - spacer + spacer - Cf6.3 FRFF - 2" scope insert. The approximate working length of this rig is ~ 100mm. I will need to test to see if I can bring the image to focus and go from there.

910mm reduced to 573mm and f7.2 is interesting... will be fun to see if this theoretical reduction is possible and practical.

Image


Stay tuned as I develop this idea, thanks for reading to the bottom.
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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